This invention has particular application to instrument pickups that utilise a single coil transducer to provide an electrical signal or “string-signal” output, corresponding to the vibrations of the strings of the instrument.
There are several types of single-coil pickups that are in widespread use in electric guitars because of the desirable individual responses they provide, causing a desired amplified sound. However these pickups in addition to providing the string-signal output also provide an unwanted output to be amplified which is induced from electrical noise external to the guitar. For example, “noise” can result from a small voltage of 50 Hz or 60 Hz induced from mains power. This noise can be most annoying to musicians and their audience.
The most popular single-coil guitar pickup in use is that standardly provided in the FENDER® STRATOCASTER® (Fender Musical Instruments Corp., 1130 Columbia Street, Brea, Calif. USA). This pickup provides coveted response characteristics that yield great sensitivity and expression in response to the various ways the guitar strings are plucked, tapped, scraped and pinched with plectrums, fingernails, or any of a wide variety of other methods used by countless guitar players throughout the world.
There have been many attempts over the decades to cancel unwanted noise in pickups which provide the response of the FENDER® Stratocaster® devices but previous methods have introduced their own set of problems and shortcomings. The valued subtle nuances of the STRATOCASTER® are often sacrificed when various noise cancelling techniques are employed.
Typically the problem of noise cancelling is tackled by providing a second coil which generates an equal and opposite noise voltage to cancel the noise voltage generated in the string-sensing pickup coil which provides the desired output to be amplified. Typically this further coil is disposed proximate to the string-sensing pickup coil.
Unfortunately this noise-sensing coil often chokes or constricts the subtle nuances of tone that are otherwise present in the string-sensing pickup coil because of excessive coil capacitance.
Another popular single coil pickup is the Gibson Guitar Company's P-90® pickup (Gibson Guitar Corp., 1818 Elm Hill Pike, Nashville, Tenn. USA). The P-90® pickup is slightly different to the FENDER® single coil pickups in that it has a different magnetic system. The FENDER® pickups utilise rod magnets beneath each string as the core of the coil whereas the P-90® pickup utilises bar magnets disposed beneath the pickup coil with six adjustable steel screws as the core of the coil which conduct the magnetic field from the magnets to the strings. The coil of the P-90® has much more inductance than any STRATOCASTER® pickup. Consequently this device generates more noise voltage than the FENDER® pickups.
It has been widely practiced that a side-by-side GIBSON® style humbucking two coil pickup has one coil shorted or disconnected for the purpose of modifying the sound to resemble that of a STRATOCASTER® single coil pickup. The disabling of the second coil also disables the noise cancelling ability of the pickup since it has been temporarily transformed into a single coil pickup. By providing a further noise sensing coil of the present invention that is switched into circuit when the second coil is disconnected the facsimile STRATOCASTER® sound can also be noise free.
The STRATOCASTER® pickup typically has between 7,800 and 8,350 turns of 0.063 (42 gauge) wire to provide a DC resistance of between 5.6K ohms and 6.1K ohms and an inductance of 2.1 and 2.5 Henrys with a Q factor of approximately 2.8, whereas the P-90® pickup typically has in the order of 8,000 to 10,000 turns of 43 gauge wire to provide a DC resistance of about 8.3K ohms and an inductance of about 6.8 Henrys and a Q factor of 2.85.
Pickups having noise-sensing coils have been manufactured by me in accordance with my earlier Australian and United States Patents (AU 2081800; AU 711540; U.S. Pat. No. 5,668,520; U.S. Pat No. 5,908,998; and U.S. Pat. No. 6,103,966). These pickups have emulated the sonic quality of a STRATOCASTER® pickup and utilise a noise-sensing coil with adequate noise-voltage/turns ratio achieved by forming the core of the noise cancelling coil of pins or rods made of magnetically permeable material, such as steel and by flanking each side of the noise sensing bobbin with unitary steel plates to boost the inductance.
While this arrangement has proved successful for the STRATOCASTER® style pickup it can be improved upon and it does not provide a noise cancelling solution to P-90® style pickups as the number of coil turns required to generate sufficient noise voltage is excessively high and the sonic degradation is correspondingly high due to the excessive capacitance of the coil.
This invention aims to provide improved noise sensing bobbin-coil assemblies for string musical instrument pickups.